To reduce the number of internal components and the degradation of the read signal, many memory devices lack dedicated pass-gate transistors to couple and uncouple the read circuits, which typically each include a sense amplifier, equilibration circuit, and data-line driver, to and from the read lines during a read cycle and a write cycle respectively. Typically, such a memory device uses the column-select gates to isolate the read circuits from the read lines. Often, such a memory device couples both the read and the write lines to the bit lines of an addressed memory cell during both a read and a write cycle. Thus, the memory device often couples the read circuits to the write lines during a write cycle. Such coupling, however, typically does not affect the reading of data from or the writing of data to the addressed memory cell.
A problem with such a memory device is that during a write cycle, each of the sense amplifiers, which the memory device does not use during a write cycle, may draw a current, often called a "crowbar" current, from the power supply. During a read cycle, the sense amplifier receives on a pair of complementary read lines the data signal from the memory cell, and amplifies the data signal on the read lines. The data-line driver receives the amplified data signal and provides it to the data line. During a write cycle, the sense amplifier has no function, and should ideally draw little or no power-supply current. During a write cycle, however, the transistors that couple the read lines to the bit lines of the addressed memory cell often generate on one of the read lines the power-supply voltage, i.e., Vcc, and generate on the remaining read line a body-effected threshold voltage that is between a logic 0 (typically 0 volts) and a logic 1 (typically 5 volts). This body-effected threshold voltage is often sufficient to activate the leg of the sense-amplifier to which it is coupled, and thus causes the sense amplifier to draw a supply current during a write cycle. The sum of such currents from all of the so-activated sense amplifiers can be significant.
These crowbar currents may be sufficient to render such a memory device unsuitable for low-power applications, such as battery applications. Furthermore, the additional heat that these currents generate may shorten the lifetime of the memory device, or necessitate more complicated heat-dissipation techniques or structures.